Process for polymerizing styrene in contact with benzoyl peroxide and di(tertiary butyl) peroxide



Patented Dec. 12, 1950 PATENT OFFICE PROCESS FOR POLYMERIZING STYRENE IN CONTACT WITH BENZOYL PEROXIDE AND DI(TERTIARY BUTYL) PEROXIDE Sanford E. Glick, Springfield, Mass., assignor to Monsanto Chemical Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Application March 13, 1948, Serial No. 14,819

4 Claims.

This invention relates to a catalyst composition for the polymerization of styrene. More particularly, the invention relates to a catalyst composition for obtaining styrene polymers having a relatively lowaverage molecular weight.

-The, most effective catalysts for promoting the polymerization of styrene are the peroxide catalysts and the best known of these and the most widely used is benzoyl peroxide. The emphasis has heretofore been placed on obtaining polymers of high average molecular weight such as 60,000. to 85,000 'for polymers to be injection molded and 100,000 to 200,000 for objects made by the casting process.

Recently it has been discovered that polymers having an average molecular wei ht of less than 20,000 are particularly useful as the basis for surface coatings and as mor'ifiers for other polymers and resins. Three'ways have been found to obtain low average molecular weight polymers. The first way is to raisev the polymerization temperature above 120? C. which results in a polymer which is rather. highly colored and has a substantial methanol soluble component. The second methodis toradically increase the amount of polymerization catalyst from a previous maximum of'ab'out 0.1% to from 0.5% to 1.0%. The products of the second process are also highly colored and contain considerable amounts of methanol soluble impurities. The third method for obtaining low averagemolecular wei ht polymers is to use sub tantial amounts of well known polymer= ization modifiers which results in material having undue softness and tack. Att mpts to use a combinationof two'or more of the cited metho s have been successful only in producing a material having anaverage molecular weightin the neighborhood of 25,000, at lea t 3% et anol soluble material and more color than desirable.

It is an object of this invention to provide a new catalyst combination.

n further object is to provide styrene polymers having an {av rage molecularw'eight below 20,000

and above 10.000. 1

V fAnothe'r object is to provide a'styrene polymer having anaverage molecular weight of below 20,000 and above 10.000 which contains less than 3% methanol soluble material and which contains a minimum of color.

These and other objects are attained by using a combination of benzoyl peroxide and di(tertiary butyl) peroxide as catalyst for the polymerization of styrene.

The following examples are given in illustration and are not intended as limitations on the scope of this invention. Where parts are mentioned, they are parts by weight.

Example I 2 hours at C. 2 hours at C. 16 hours at C.

At the end of the polymerization cycle a clear, colorless polystyrene was obtained, which on analysis proved to have an average molecular weight of 17,000. It contained 2.3% methanol solubles.

Example II 100 parts of refined styrene monomer were mixed with 0.3 part of benzoyl peroxide and 0.005 part of di(tertiary butyl) peroxide and the mixture was polymerized in a sealed glass container according to the same schedule as in Example I. The resulting polym r had an average molecular weight of about 19,000 and a methanol soluble content of about 1.9%.

Example III Example IV 100 parts of refined styrene monomer were mixedwith 0.7 part'of benzoyl peroxideand 0.05 part" of di(tertiary butyl) peroxide and the mixture was polymerized as above. The resulting polymer had an average molecular weight of 13,000 and a methanol soluble content of less than 2%.

Example V 100 parts of refined styrene monomer were mixed with 0.5 part of benzoyl peroxide but no di(tertiary butyl) peroxide was used. The mixture was polymerized as above and yielded a polymer having an average molecular weight of 23,000

and a methanol soluble content of more than 3%. These results are in marked contrast with the results obtained in the previous examples in that the molecular weight is from 30 to 75% higher and the methanol soluble content is also substantially higher and in the range of non-acceptable products, i. e., a methanol soluble content of 3% or higher.

The catalyst compositions of this invention comprise benzoyl peroxide and di(tertiary butyl) peroxide in which the benzoyl peroxide is the major component. Based on 100 parts of benzoyl peroxide the di(tertiary butyl) peroxide content may vary from about 0.7 to about 7 parts. Based on 1.00 parts of styrene monomer the benzoyl peroxide may vary from about 0.3 part to about 0.7 part and the di (tertiary butyl) peroxide may vary between about 0.002 and 0.05 part.

The polymerization temperature may be varied between about 120 C. and about 200 C. Temperature may be applied stepwise as shown in the examples or a grad al rise in temperature may be used. It is preferable but not neces ary to s art the polymerization at the lower end of the temperature ran e and finish near the higher end of the range. Thus. it is perfectly fea ible to conduct the entire polvmerization at 120 0., in which case, the durat on of t e polymerization mu t he con derably ex ended to be complete and the methanol soluhle content is likely to be on the high side. Conver ely, the entire polymerization may he condu ted at or near 180 C. Und r the e condition the polymerization is verv ra id and con derable pre sure and heat is developed. The pol mer re ui ing will be in the lower average molecular wei ht ran e and the color of the product is ant to be reater. The pre erred process of th s in ention is to nolvmerize t e styrene at tem ratures below 150 C. for from 2 to 6 ho rs and t en to fini h the process at t mperatures above 1 C. to a out 200 C.

The catalvst compo it on and the proce s 01' this invention ma al o he a pl ed to obtaining low avera e molecular we ht pol mers of styrenes sub tituted in the ring or in the side chain by or anic and inorganic radicals as well as copoivmer of styrene and or sub tituted stvrenes with other com ounds polvmerizable therewith in which the styrene or substituted st rene is the ma or component. For example, low average mole ular we g t pol mers may be prepared using the catalvss and the proce s of this invention from mono and polv halostvrene monomers such as monochloro tyrene. di hloro tyrenes, from mono and poly alkyl styrenes such as p-ethvl. p-methyl o.n-dimethy1, p-methyl-alnhamethyl al ha-methyl styrenes. etc. Examples of ful in producing styrene polymers having an average molecular weight between about 10,000 and 20,000 which contain less than 3% methanol solubles and a minimum of developed color.

It is obvious that many variations may be made in the products and processes of this invention without departing from the spirit and scope thereof as defined in the appended claims.

What is claimed is:

1. A process for preparing homopolymers of styrene having an average molecular weight of from 10,000 to 20,000 which consists essentially of polymerizing parts of styrene in contact with a catalyst consisting of 100 parts of benzoyl peroxide and from 0.7 to 7.0 parts of di(tertiary butyl) peroxide, the ratio of styrene to benzoyl peroxide varying from 10020.3 to 100:0.7, the polymerization react on being carried out at temperatures of -200 C.

2. A process for preparing a homopolymer of styrene having an average molecular weight 01' 17 000 which con ists of polvmerizing 100 parts of styrene in contact with 0.5 part of benzoyl peroxide and 0.01 part of di tertiary butyl) peroxide, by heating according to the following schedule:

2 hours at C. 2 hours at C. 16 hours at C.

3. A process for preparing a homopolymer of styrene having an average molecular weight of about 15.000 which consists of polymerizing 100 parts of st rene in contact with 0.7 part of henzoyl peroxide and 0.005 part of di(tertiary butyl) perox de. by heating according to the following schedule:

2 hours at 130 C. 2 hours at 145 C. 16 hours at 165 C.

4. A process for preparing a homopolymer of styrene having an avera e molecular weight of about 13.000 which consists of polymerizing 100 parts of styrene in contact with 0.7 part of hen-- zoyl peroxide and 0.05 part 01' di(tertiary butyl) peroxide, by heating according to the following schedule:

2 hours at130 C. 2 hours at 145 C. 16 hours at 165 C.

SANFORD E. GLICK.

REFERENCES CITED' The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,979,187 Bindley Oct. 30, 1934 2,136,167 Higgins Nov. 8, 1938 2,359 196 Britton et al Sept. 26, 1944 2,367,805 Semple Jan. 23, 1945 2,426,476 Vaughan Aug. 26, 1947 2,430,993 Rehner Nov. 18, 1947 2,444,655 Kroeker et a1. July 6, 1948 

1. PROCESS FOR PREPARING HOMOLPOLYMERS OF STYRENE HAVING AN AVERAGE MOLECULAR WEIGHT OF FROM 10,000 TO 20,000 WHICH CONSISTS ESSENTIALLY OF POLYMERIZING 100 PARTS OF STYRENE IN CONTRACT WITH A CATALYST CONSISTING OF 100 PARTS OF BENZOYL PEROXIDE AND FROM 0.7 TO 7.0 PARTS OF DI(TERTIARY BUTYL) PEROXIDE, THE RATIO OF STYRENE TO BENZOYL PEROXIDE VARYING FROM 100:0.3 TO 100:0.7, THE POLYMERIZATION REACTION BEING CARRIED OUT AT TEMPERATURES OF 120-200*C. 